Residents walk past a banner reading "Welcome to the Philippines, Province of China" on an overpass along the C5 road intersection in Taguig, Metro Manila

Residents walk past a banner reading "Welcome to the Philippines, Province of China" on an overpass along the C5 road intersection in Taguig, Metro Manila, Philippines July 12, 2018. REUTERS/Erik De Castro

MANILA (Reuters) - Banners calling the Philippines a "province of China" mysteriously appeared on bridges in Manila on Thursday, sparking fury on social media on what was the second anniversary of Manila's victory over Beijing in a landmark arbitration case.

The terms "province of China" and "South China Sea" trended prominently on Twitter, while news reports of the sudden appearance of the red tarpaulin banners along key thoroughfares generated thousands of shares and comments on Facebook.

No group claimed responsibility for the banners, which feature English and Chinese characters and a Chinese flag flanked by dragons. City authorities were seen removing some of them, which were spotted in at least five locations.

Emojis denoting anger or surprise dominated comments on social media next to pictures of the signs, which say "Welcome to the Philippines, Province of China".

The Permanent Court of Arbitration in The Hague ruled two years ago that China had no historic title over the waters of the South China Sea and it had breached the Philippines' sovereign rights by blocking its fishermen and building artificial islands in its Exclusive Economic Zone.

"NOT FUNNY", former solicitor general and chief lawyer for the Philippine case, Florin Hilbay, posted on his social media accounts.

Some users accused the political opposition of making the signs to discredit the government's warming ties with China.

Other chided the government for not challenging China's assertiveness in the South China Sea. "This is too much. The country was sold off," one Facebook user said.

The two countries have a bitter history of disputes over maritime sovereignty, but under President Rodrigo Duterte, who took office just two weeks before the Hague ruling, Manila has taken a conciliatory approach and wants China's loans, trade and investments.

Duterte frequently praises Chinese counterpart Xi Jinping and in February caused a stir when he jokingly offered the Philippines to Beijing as a province of China.

The Philippines scored an "own goal" in its failure to press China to implement the arbitration ruling, opposition party Akbayan said.

During an event to mark the anniversary of the ruling, Vice President Leni Robredo, who was elected separately to Duterte, said Filipinos should peacefully protest against the government's inaction.

Duterte's spokesman, Harry Roque, called the banners "absurd" and said it was likely the government's political enemies were behind them.

China's foreign ministry did not immediately respond to a request for comment.